Influenza is a respiratory infection that causes severe health problems. The worldwide spread of the A/H5N1 avian flu and the outbreak of the new type A/H1N1 human influenza in 2009 have increased public awareness of the potential for global influenza pandemics. H5N1 influenza virus appears to replicate more rapidly than seasonal influenza and the pandemic H1N1/2009 strain. The H5N1 virus infection of macrophages also causes strong expression of proinflammatory cytokines and chemokines, namely cytokine storm. (Lee, S. M. Y. et al. J. Infect. Dis. 2008, 198, 525; Woo, P. C. Y. et al. J. Infec. Dis. 2010, 201, 346)
In the patients of H5N1 virus infection, induction of tumor necrosis factor (TNF)-α and interferons (IFN)-β/γ have been observed in alveolar and bronchial epithelial cells. (Yuen, K. Y. et al. Hong Kong Med. J. 11, 189 (2005)) Other cytokines, such as interleukins (e.g. IL-6 and IL-10), IFN-induced chemokines (e.g. IP-10, MIG and MIG-1) are also found at high levels in the H5N1 virus infected patients. (de Jong, M. D. et al. Nat Med 2005, 11, 189) The high mortality of human infected by influenza H5N1 has been attributed to poor response of virus to neuraminidase (NA) inhibitor, e.g. oseltamivir, and the excessive induction of a severe cytokine storm. (Peiris, J. S. M. et al. Lancet 2004, 363, 617; Geiler, J., Med. Microbiol. Immunol. 2011, 200, 53) Though treatment of the H5N1 virus infected mice with anti-inflammatory agent alone can inhibit proinflammatory cytokines, (Fedson, D. S. Influenza Other Resp. 2009, 3, 129) the mortality of infected mice is not reduced. (Carter, M. J. A J. Med. Microbiol. 2007, 56, 875; Salomon, R. et al. Proc. Natl. Acad. Sci. U.S.A. 2007, 104, 12479)
Monotherapy with a single antiviral drug for influenza may be limited in efficacy due to the rapidly developed drug-resistance. (Baz, M. et al. New Engl. J. Med. 2009, 361, 2296). Moreover, the uncontrolled virus-induced cytokines could cause the high mortality of human infected by H5N1 avian influenza virus.
In a different approach, combination chemotherapy consisting of two or more drugs that target different viral proteins or host immune response may provide additive or synergistic antiviral activities, (Govorkova, E. A. & Webster, R. G. Viruses 2010, 2, 1510) and thus reduce the risk of drug-resistance with monotherapy.
Zanamivir (ZA) is a potent influenza virus neuraminidase (NA) inhibitor, known as Relenza™ on market; (Ryan, D. M. et al. Antimicrob. Agents Chemother. 1994, 38, 2270) the viral resistance to zanamivir is rare. (Collins, P. J. et al. Nature 2008, 453, 1258-1261). Zanamivir combined with triamcinolone, an anti-inflammatory corticosteroid, has been applied to treat H3N2 virus infection. (Ottolini, M. et al. Pediatr. Pulmonol. 2003, 36, 290) In another study, (Zheng, B. J. et al. Proc. Natl. Acad. Sci. USA 2008, 105, 8091) the mice inflected with highly virulent H5N1 virus (1000 LD50) receiving a triple combination of zanamivir with immuno-modulating drugs (celocoxib and mesalazine) showed better survival rate in comparison with the treatment with zanamivir alone. The enhanced therapeutic effect may be attributable to the synergistic antiviral activity and cytokine suppression.
Therefore, there is a need for newer and synergistically effective bifunctional drugs for the prophylaxis, treatment and therapy of influenza virus infection where the drugs are formed by conjugation of an anti-influenza moiety with a moiety that suppresses pro-inflammatory cytokines.